Erik Koeppel using a cigar box.
Historic system. Box with multiple panels, palette, paints, brushes etc. Sit on a chair put it on lap and paint.
Take it easel, US made. an extension to the Anderson Gloucester easel. Probably the sturdiest easel.
Beauport easel, China made again an extension to Anderson easel. This is also very sturdy.
Mabef M/29 field easel
Franch box easel. Most commonly used.Stefan Baumann suggests to buy only Mabef or Julian.
Open Box M. Another most commonly used.
Jullian (marketed by Utrecht)
Thumb box. Has a thumb holder below to get rid- of tripods. Holds 5X7
inches panels. Derived from cigar boxes used by olden day artists.
Coulter Plein Air System
For those who are in Russia, Yarka box easel
Edge Pro PaintBook easel